Multi-protocol label switching (MPLS) operates at a layer between a link layer and a network layer that are in a TCP/IP protocol stack, and is used for providing a connection service to an Internet Protocol (IP) layer, and also obtaining a service from the link layer. The MPLS uses label switching instead of IP forwarding. A label is a short connection identifier with a fixed length and a local meaning only. The label header is encapsulated between the link layer header and the network layer header. The MPLS is not limited to any specific link layer protocol, and can transmit a network packet by using any layer-2 medium. The MPLS is not a service or an application, and is actually a tunneling technology. This technology not only supports multiple upper-layer protocols and services, but also may guarantee security of information transmission to an extent. The Label Distribution Protocol (LDP) is a control protocol of multi-protocol label switching MPLS, is equivalent to a signaling protocol in a conventional network, and is responsible for operations such as classifying a forwarding equivalence class (FEC), allocating a label, and establishing and maintaining a label switched path (LSP). The LDP stipulates various messages and relevant processing procedures in a label distribution process.
The MPLS supports labels of multiple layers, and is connection-oriented on a forwarding plane, and therefore has high scalability, so that it becomes possible to provide various services for a customer on a uniform MPLS/IP network infrastructure. By using the LDP protocol, a label switched router (LSR) may directly map routing information of a network layer to a switched path of a data link layer, so as to establish an LSP of the network layer. Currently, the LDP is widely applied in VPN services, and has advantages such as simple networking and configuration, supporting a route topology-driven establishment of an LSP, and supporting a large-capacity LSP.
A virtual private network (VPN) is a virtual private communications network established in a public network in dependence on an Internet service provider (ISP) and a network service provider (NSP). A basic principle of the VPN is: a VPN packet is encapsulated in a tunnel by using the tunneling technology, and a private data transmission channel is established by using a VPN backbone network, so as to transparently transmit the packet. The tunneling technology uses a protocol for encapsulating a packet of another protocol, and an encapsulation protocol itself may be also encapsulated or carried by another encapsulation protocol.
A BGP/MPLS IP VPN is a Layer 3 Virtual Private Network (L3VPN) that uses the Border Gateway Protocol (BGP) to publish a VPN route on a service provider backbone network, and uses MPLS to forward a VPN packet on the service provider backbone network. IP herein refers to that the VPN carries an IP packet.
Pseudo-wire emulation edge to edge (PWE3) is a mechanism for emulating, on a PSN network, key attributes of services such as asynchronous transfer mode (ATM), frame relay (FR), and Ethernet services. The PWE3 may enable an operator to migrate a conventional service to the packet switched network PSN to reduce network operating costs.
To guarantee high availability of a service, different layers of a network all need to support redundancy: when a fault occurs in a resource such as a network node, a link, or a channel that is currently in use, the service can be switched to another redundant available resource, so as to guarantee that the network can continue to provide the service as stipulated.
LDP FRR is a fast protection method in which a protection path of a tunnel is calculated in advance, and a data packet is switched to a backup path immediately after a fault of a primary path is detected. The LDP FRR may perform protection for a node and a link, and the protection is always initiated by a faulty upstream neighbor, and different nodes establish different protection paths for a downstream node. Because a path or tunnel from an ingress node to an egress node is generally long, a relatively long switching time is needed after an upstream node initiates protection switching until the path is switched.